1 files changed, 48 insertions, 0 deletions
diff --git a/include/o3tl/char16_t2wchar_t.hxx b/include/o3tl/char16_t2wchar_t.hxx
new file mode 100644
index 0000000000..c2640f6271
--- /dev/null
+++ b/include/o3tl/char16_t2wchar_t.hxx
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#pragma once
+
+#include <sal/config.h>
+
+#include <string_view>
+
+namespace o3tl
+{
+#if defined _WIN32
+// Helpers for safe conversion between wchar_t and char16_t in MSVC
+
+static_assert(sizeof(char16_t) == sizeof(wchar_t),
+              "These helper functions are only applicable to implementations with 16-bit wchar_t");
+
+// While other implementations define wchar_t as 32-bit integral value, and mostly use
+// char-based UTF-8 string APIs, in MSVC wchar_t is (non-conformant) 16-bit, and Unicode
+// support is implemented by Unicode-aware WinAPI functions taking UTF-16 LE strings,
+// and also stdlib functions taking those strings.
+//
+// In LibreOffice, internal string representation is also UTF-16 with system endianness
+// (sal_Unicode that is typedef for char16_t); so it is an important implementation concept
+// to treat internal strings as directly usable by WinAPI/stdlib functions and vice versa.
+// Also, it's important to use safe conversion between unrelated underlying C++ types
+// used for MSVC and LibreOffice string storage without plain reinterpret_cast that brings
+// risks of masking errors like casting char buffers to wchar_t/char16_t.
+//
+// Use these helpers for wchar_t (WSTR, WCHAR, OLESTR etc) to char16_t (sal_Unicode) string
+// conversions instead of reinterpret-cast in Windows-specific code.
+inline wchar_t* toW(char16_t* p) { return reinterpret_cast<wchar_t*>(p); }
+inline wchar_t const* toW(char16_t const* p) { return reinterpret_cast<wchar_t const*>(p); }
+inline char16_t* toU(wchar_t* p) { return reinterpret_cast<char16_t*>(p); }
+inline char16_t const* toU(wchar_t const* p) { return reinterpret_cast<char16_t const*>(p); }
+
+inline std::u16string_view toU(std::wstring_view v) { return { toU(v.data()), v.size() }; }
+inline std::wstring_view toW(std::u16string_view v) { return { toW(v.data()), v.size() }; }
+#endif
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */